Semiconductor device package utilizing proud interconnect material

ABSTRACT

A semiconductor package which includes a conductive can, a semiconductor die received in the interior of the can and connected to an interior portion thereof at one of its sides, at least one interconnect structure formed on the other side of the semiconductor die, and a passivation layer disposed on the other side of the semiconductor die around the interconnect structure and extending at least to the can.

RELATED APPLICATION

This application is a division of U.S. application Ser. No. 10/970,557,filed Oct. 21, 2004 entitled Semiconductor Device Package UtilizingProud Interconnect Material which is based on and claims priority toU.S. Provisional Application No. 60/514,095 filed Oct. 24, 2003,entitled Solder and Solder Process and No Flow/Reflowing Interconnectsand U.S. Provisional Application No. 60/555,794, filed Mar. 24, 2004,entitled Semiconductor Device Package Utilizing Proud InterconnectMaterial.

FIELD OF THE INVENTION

The present invention relates to semiconductor packaging, and moreparticularly to an interconnect structure and a paste for forming theinterconnect structure.

BACKGROUND OF THE INVENTION

Solder is a conventionally known material for connecting a semiconductordevice to a conductive pad on a circuit board. According to a well knowntechnique, solder bumps can be formed on a conductive pad of a circuitboard, a component such as a semiconductor die can be placed thereon,and the solder is then reflown in order to connect the component to theconductive pad. Alternatively, the solder bump can be formed on thesemiconductor component, the component can be placed on the conductivepad, and the solder reflown to connect the component to the conductivepad.

Referring to FIG. 1 for illustrative purposes, to form a solder bump ona conductive pad 14 of a circuit board 10, first a solder paste 15 isdeposited on a portion of conductive pad 14. As shown in FIG. 1, todefine the area that receives solder paste 15, a solder mask 12 may beapplied to the top surface of circuit board 10 which includes an openingover conductive pad 14.

Referring to FIG. 2, after depositing solder paste 15 over conductivepad 14, solder paste 15 is reflown by applying heat; i.e. by taking thesolder paste to its reflow temperature to form a liquidous. After theliquidous is cooled, a solder bump 17 is formed over conductive pad 14.It should be noted that solder bump 17 has a curved outer surface 19.Curved outer surface 19 is due to the surface tension when the solder isreflown, and becomes more curved as the volume of solder is increased.Thus, to join a component and a conductive pad on a circuit board usingthe conventional technique described herein the stenciling of the solderon the circuit board (or the component) requires strict adherence tocertain tolerances which complicates manufacturing.

SUMMARY OF THE INVENTION

According to the present invention a paste is used to form interconnectsfor electrically connecting components to one another or to conductivepads on a circuit board or the like.

A paste according to the present invention is a mixture of binderparticles and filler particles, and, where required, a flux material.According to the present invention binder particles melt at a lowertemperature than the filler particles. Furthermore, the respectiveproportion of the binder particles and the filler particles is such thatwhen binder particles are melted the shape of the paste as depositeddoes not change substantially but there is enough to glue the fillerparticles to one another after the binder liquidous is cooled in orderto form a structure. A structure so formed can serve as an interconnect.Thus, a paste according to the present invention can be used to forminterconnect structures on a surface, such as an electrode of asemiconductor component or a conductive pad on a circuit board.

An interconnect according to the present invention can cover a largearea on, for example, an electrode of a power semiconductor device.Also, such an interconnect can be made proud, i.e. standing above thenon-solderable surrounding area, which is advantageous because:

1) It allows the solder fillet to be less critical, which means that thesubstrate and stencil designs are less important in terms of design andtolerance in that instead of forming a solder joint between two planarsurfaces (in which the solderable area is defined by a window within asolder mask) the “proud interconnect” enables the fillet formation toinclude the edge of the solder interconnect.

2) Fundamentally forming thick interconnects onto the die surface meansthat the die surface and edge can be covered with an epoxy or any othersuitable passivation material, which is advantageous for the followingreasons:

a) The passivation enables insulation between different potentials onthe die, allowing for higher voltages and more radical designs.

b) It is likely to lead to the reduction in the process steps needed toprotect the die in certain package types.

c) It will produce a more rugged device.

d) It will provide for better environmental protection.

e) It will reduce critical manufacturing tolerances, and therefore makesthe device easier to produce.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate a technique for forming solder bumpinterconnects according to the prior art.

FIG. 3 illustrates a portion of the body of an interconnect formed witha paste according to the present invention.

FIGS. 4 and 5 illustrate a technique for forming interconnects accordingto the present invention.

FIG. 6 shows a cross-sectional view of a package according to prior art.

FIG. 7 shows a cross-sectional view of a first embodiment of a packagemodified to include an interconnect according to the present invention.

FIG. 8 shows a side plan view of a second embodiment of a package thatincludes an interconnect according to the present invention.

FIG. 9 shows a side plan view of a third embodiment of a package thatincludes an interconnect according to the present invention.

FIG. 10 shows a top plan view of a semiconductor die modified to includeinterconnects on electrodes thereof.

FIG. 11 shows a side plan view of the semiconductor die shown in FIG. 10seen in the direction of the arrows 11-11.

FIG. 12 shows a perspective view of a first variation of a packageformed with a semiconductor die which includes interconnects formedaccording to the present invention.

FIG. 13 shows a perspective view of a second variation of a packageformed with a semiconductor die which includes interconnects formedaccording to the present invention.

FIG. 14 shows a cross-sectional view of the package shown by FIG. 13along line 14-14 viewed in the direction of the arrows.

FIG. 15 shows a cross-sectional view of a package according to the priorart.

FIG. 16 shows a top plan view of a flip-chip semiconductor device whichincludes interconnects formed according to the present invention.

FIG. 17 illustrates a wafer containing die prepared to haveinterconnects according to the present invention.

FIG. 18A illustrates a cross-sectional view of a package according tothe prior art as connected to a circuit board.

FIG. 18B illustrates a cross-sectional view of a package according tothe present invention as connected to a circuit board.

DETAILED DESCRIPTION OF THE INVENTION

An electrically conductive paste according to the present inventionincludes a mixture of binder particles, and filler particles. In apreferred embodiment of the present invention, the binder particles aresolder powder, and the filler particles are conductive particlesdispersed throughout, or mixed in with the solder powder. The preferredembodiment further includes a solder flux material.

According to an aspect of the present invention, the proportion of thebinder particles relative to the proportion of the filler particles issuch that when the binder particles melt, there will be sufficientbinder to fuse the filler particles, i.e., “glue” the filler particlestogether. However, the respective portions will be such that when binderparticles are melted the shape of the paste as deposited will not changesubstantially. That is, the interconnect will substantially have thesame shape as the paste when it is deposited.

The filler particles used in a paste according to the present inventionare preferably spherically shaped, although other shapes such as cubesand parallelepipeds, or the like may also be used. It should be notedthat to practice the present invention, the shape of the particles doesnot need to be perfect geometrically. That is, for example, a sphericalshape as referred to herein need only be generally sphere-like ratherthan spherical perfectly to be within the present invention. Thus, theshape of particles as described herein should not be understood torestrict the invention to perfect geometric shape.

In the preferred embodiment, the binder has a high melting temperature.Solders formed from the combination of 95% Sn and 5%, Sb (by weight), orthe combination of 95.5% Sn, 3.8% Ag, and 0.7% Cu (by weight) areexamples of solders suitable to be used as binder material in a pasteaccording to the present invention.

A suitable material for forming the fillers is copper. Other suitablematerials for forming the fillers are nickel and tin-silver.

Referring to FIG. 3, filler particles 16 may be formed of one material 5and coated with another material 7. For example, sphere-like copperparticles, when used as conductive fillers, may be plated with a nickelbarrier and passivated with tin or silver. Suitable binders to be usedwith sphere-like copper particles are tin-silver solders, high leadsolders, or a tin-lead solder.

Sphere-like nickel particles, when used as conductive fillers, may bepassivated with tin or silver. A suitable binder for fusing sphere-likenickel particles may be any one of the solders listed above.

A suitable binder for use with tin-silver filler particles may be atin-bismuth solder.

In a preferred composition, fillers may be spherical or sphere-like andmay constitute 5-40% of the total weight of the mixture, and the bindermay be solder in powder form and constitute 50-85% of the total weightof the mixture. In this preferred composition, about 10% of the totalweight may be a solder flux which may be a resin with mild activation.Preferably, the filler particles are anywhere between 15 μm-65 μm andthe particle size of the solder binder may be anywhere between 25 μm-45μm.

One specific example of a paste according to the present inventionincludes 31.5% (by weight) of silver coated nickel particles, 58.5% (byweight) of SAC (Tin-Silver-Copper) or SA (Tin-Silver) alloys as binder.The SAC composition may be 95.5% Sn, 3.8% Ag, and 0.7% Cu (by weight),while SA composition is 96% Sn and 4% Ag (by weight). In this example,10% of the total weight may be flux material.

Another example may be a high flow derivative of the previous examplehaving anti-slump properties. Such a solder paste may include 5% (byweight) of silver coated nickel spheres, 85% SAC or SA, and 10% (byweight) of flux.

A paste according to the present invention is particularly useful forforming relatively flat large area interconnects on surfaces, such asconductive pads on a substrate, or an electrode of a semiconductor die.An advantageous characteristic of a paste according to the presentinvention is that when it is formed to a shape, it substantially retainsthat shape after the application of heat to reflow, i.e. melt, thebinder.

Referring now to FIGS. 3, 4 and 5, a process for manufacturing aninterconnect according to the present invention involves depositing anamount of a paste according to the present invention on a surface.Specifically, for example, a desired amount of a paste according to thepresent invention may be deposited over a conductive pad 14 on a circuitboard 10. Circuit board 10 may have a solder mask 12 disposed thereonsurrounding conductive pad 14. A paste according to the presentinvention which includes spherical or sphere-like filler particles 16and particles of an electrically conductive binder 18 is deposited onconductive pad 14 and extends above solder mask 12. The paste may be sodeposited to have a relatively flat top as shown in FIG. 4. In thepreferred embodiment, a paste according to the present invention may bedeposited using a stenciling or printing method, although other methodsof deposit are considered within the invention.

After depositing the paste, heat is applied to cause binder particles 18to melt. Thus, if solder is used as a binder, heat is applied until thesolder is reflown, i.e. the solder is taken to its reflow temperature.Since, binder particles 18 have a much lower temperature than fillerparticles 16, filler particles 16 remain solid. However, binderparticles 18 melt and wet filler particles 16. Once the temperature islowered below the melting temperature of binder particles 18, fillerparticles 16 are “glued” to one another, thereby forming an integralstructure as shown in FIGS. 3 and 5.

According to one aspect of the present invention, the proportion ofbinder particles is so selected that there will not be enough liquidousto flow, but there will be enough liquidous to glue filler particles 16together to form an integral structure suitable to serve as aninterconnect.

Advantageously, it has been found that a paste according to the presentinvention substantially retains its shape as deposited after the binderhas melted and solidified. Thus, a paste according to the presentinvention is ideal for forming interconnects with exterior surfaces ofreduced curvature and/or reduced hot-slumping property for electricalconnection to external elements, which is a desirable characteristic foran interconnect.

Referring now to FIG. 6, a package according to the prior art includes afirst circuit board 20, a second circuit board 22, a semiconductor die24 which is disposed between first and second circuit boards 20, 22 andelectrically connected to respective conductive pads 21 on each circuitboard 20, 22 by solder 26 or the like. A package as shown in FIG. 6 alsoincludes an interconnect 28, which may be a copper slug, thatinterconnects first and second circuit boards 20, 22 through respectivelayers of solder 26 or the like. A more detailed description of apackage according to FIG. 6 is shown in published U.S. PatentApplication No. 2004/0119148A1, assigned to the assignee of the presentinvention the subject matter of which is hereby incorporated byreference.

According to another aspect of the present invention, interconnect 28may be formed according to the present invention. Specifically,referring to FIG. 7, an interconnect structure 19 may be used instead ofan interconnect 28 in a package according to FIG. 6.

Referring now to FIG. 8, in an alternative embodiment, an interconnect19 may be used for external connection. Specifically, an interconnect 19may be formed according to a method of the present invention to have aconnection surface 21. Connection surface 21 is left free so that it maymake connection to an external element such as a conductive pad on acircuit board. Note that in the example shown by FIG. 8, a firstsemiconductor component 30 and a second semiconductor component 32 arealso connected to respective conductive pads 21 on circuit board 20 by alayer of solder 26. Semiconductor components 30, 32 also include freeconnection surfaces 31, 33, which are preferably coplanar withconnection surface 21 of interconnect 19. Similar to connection surface21, free connection surfaces 31, 33 of semiconductor components 30, 32may be adapted for direct connection to conductive pads of a circuitboard. For example, free surfaces 31, 33 may be made solderable.

Semiconductor components 30, 32 may be power MOSFETs, diodes, IGBTs, orany other semiconductor device such as a control IC, or the like, andcircuit board 20 may be a thermally conductive circuit board such as aninsulated metal substrate (IMS). It should be noted that in theembodiment shown by FIG. 8, insulation 34 may be formed in the gapsbetween semiconductor components 30, 32 and semiconductor components andinterconnect 19. Insulation 34 may be composed of, for example,polyimide, BCB, epoxy based dielectrics silicon polyesters, ororganopolysiloxanes.

Referring now to FIG. 9, in another embodiment, which resembles theembodiment shown in both FIGS. 6, and 7, a package may include aninterconnect 19 formed according to the present invention on a firstcircuit board 20, and a second circuit board 22 may be provided with asolderable free surface 36. Solderable free surface 36 may beelectrically connected to semiconductor components 30, 32 and serve asan external connection surface for electrically connecting semiconductorcomponents 30, 32 to respective external elements such as respectiveconductive pads on a circuit board. Solderable free surface 36 may beelectrically connected to semiconductor components 30, 32, through vias(not shown) or the like in circuit board 22 as is conventionally known.Preferably, solderable free surface 36 and free connection surface 21 ofinterconnect 19 are coplanar to facilitate the surface mounting of apackage according to FIG. 9.

Referring now to FIGS. 10 and 11, an interconnect 19 according to thepresent invention can be formed on an electrode of a semiconductordevice such as a power MOSFET 40. Specifically, for example, aninterconnect 19 can be formed on source electrode 42 and gate electrode44 of a power MOSFET 40.

According to an aspect of the invention, a plurality of MOSFETs 40 canbe formed in a wafer, a paste according to the present invention can beformed on respective electrodes of power MOSFETs 40 while in the wafer,and then subjected to heat to form interconnects 19. Thereafter, powerMOSFETs 40 may be singulated by, for example, sawing or some otherconventional method to obtain individual power MOSFETs, such as the oneshown by FIGS. 10 and 11. Thus, interconnects 19 can be formed at waferlevel prior to the packaging of power MOSFET 40.

Referring next to FIG. 12, a power MOSFET 40, according to the presentinvention may be packaged in a conductive can 48 according to analternative embodiment. Specifically, drain electrode 43 of a powerMOSFET 40 may be electrically connected to the inside surface of can 48to form a new chip-scale package similar to a prior art packagedisclosed in U.S. Pat. No. 6,624,522 the disclosure of which isincorporated by reference.

In a first variation, MOSFET 40 includes interconnect 19′ formedaccording to the present invention on source electrode 42 of MOSFET 40,and interconnect 19″ on gate electrode 44 of MOSFET 40 without anypassivation. Thus, there will be no passivation on the free surface(surface not covered by interconnects 19′, 19″) of power MOSFET 40, andthere will be a gap between the edges of power MOSFET 40 and thesurrounding walls 49 of can 48 as seen in FIG. 12. It should be notedthat MOSFET 40 may be made thinner than the depth of can 48 in that theheight of interconnects 19′, 19″ may be designed to ensure coplanaritywith external connection surfaces 51 of can 48, which are used toelectrically connect can 48 to, for example, conductive pads on acircuit board. The option of reducing the thickness of MOSFET 40 isadvantageous in that it may allow reduction of its ON resistance.

Referring now to FIG. 13, in a second variation, a passivation structure50 is formed over the free surface of power MOSFET 40, which ispreferably extended to cover the gap between the edges of power MOSFET40 and surrounding walls 49 of can 48. Passivation structure 50 ispreferably formed from a silicon organic polymer material, such assilicon/epoxy or silicon/polyester which belong to the family oforganopolysiloxanes. The use of such materials is advantageous due totheir high temperature and moisture resistance. A preferred material isthe combination of silicon epoxy, silicon polyester, acrylate, a thermalcatalyst, and a UV monomer partial catalyst. A passivation formed fromsilicon epoxies or silicon polyesters is preferred because it is highlyresistant to solvents and other chemicals, and provides high levels ofboth environmental and dielectric protection at a very modest thickness,e.g. a few microns.

Referring to FIG. 14, it should be appreciated that when passivationstructure 50 is formed, tracking distance 52 becomes the distancebetween an interconnect 19′ and the closest wall 49 of can 48. Thus,compared to a prior art package (see FIG. 15) tracking distance 52 iswider in that in the prior art package tracking distance 52 is thedistance between the edge of the power MOSFET and the electrodesdisposed on the die surface. The increase in the width of trackingdistance 52 enables can 48 to be used with power MOSFETs of voltageratings higher than 100V when an small can is used and even 300V orhigher power MOSFETs in other types of cans. Furthermore, anarrangement, such as the one shown by FIGS. 12 and 13, allows for largerpads on low voltage devices, which improves the thermal characteristics,and the ON resistance (Rdson) of the package, and reduces the currentdensity in the solder joints when the package is installed.

In a preferred embodiment, interconnects 19′, 19″ in a package accordingto FIGS. 12 and 13 are formed from a paste formulated with a lead-freesolder as a binder, and spherical or sphere-like nickel particles whichare coated with silver as filler particles. A preferred lead free solderalloy may be composed of 96% Sn, 4% Ag, 0.7% Cu (by weight). Inaddition, in the preferred embodiment the spherical nickel particles mayhave a mean diameter of 45 microns. It should be noted that althoughnickel particles are spherical in shape, the silver coating may renderthe exterior surface thereof irregular.

The combination of silver-plated nickel spheres and tin-silver basedsolder is preferred for at least the following reasons:

1. The solder alloy picks up additional silver from the silver coatednickel particles during the reflowing process, which changes thecomposition in the solder alloy. The change in composition results in anelevated fully liquid temperature for the solder, which is advantageousas it means that the solder does not become fully liquid duringsecondary soldering of the interconnect. Thus, the interconnectmaintains its shape after it is joined to a conductive pad with a layerof solder.

2. The nickel particles are very hard and can form an effective barrierfor strengthening interfaces. A paste according to the inventioneffectively forms a conglomerate and is therefore more resistant toflexing and deformation than the base solder, i.e. binder material. Thatis, it is stronger than the base solder. However, it is also effectivelymore brittle than the base solder and when pushed outside its elasticrange it may propagate minor failure sites within its body. Whereasconventional lead-free solders tend to feed the stress into the solderinterface layers, an interconnect according to the present inventionabsorbs the stress within its body. Therefore, in many cases, aninterconnect according to the present invention acts as asemi-sacrificial layer to the surface it has joined.

A package according to the variations shown in FIGS. 12 and 13, is firstformed by forming interconnects 19′,19″ on respective electrodes of apower MOSFET 40 prior to mounting the power MOSFET on the interiorsurface of can 48. Specifically, first, a plurality of power MOSFETs 40are formed in a wafer. Thereafter, interconnects 19′ are formed onsource electrodes 42 of power MOSFETs 40, and interconnects 19″ areformed on gate electrodes 44 of power MOSFETs 40. Preferably, to forminterconnects 19′,19″ a paste according to the present invention isdeposited through a stencil onto source electrodes 42 and gate electrode44 of each MOSFET 40 respectively. Using a stencil is a well knownprocess in the manufacturing of printed circuit boards and is alsowidely used for forming solder balls on conventional flip-chip typedevices. Alternatively, the paste for forming interconnects 19′,19″according to the present invention could be deposited using any othermethod that would result in the paste being shaped during thedeposition, such as solder casting or molding.

Preferably, a wafer processed according to the present invention doesnot include any passivation schemes over and above those generally usedon the die. However, the process will not exclude wafers that have beentreated with all currently available passivations used in themanufacture of power semiconductor devices.

After depositing the paste the wafer is subjected to heat in order toreflow the binder. Preferably, the wafer is heated in a convectionreflow oven, which is a process used typically in printed circuit boardassembly. Preferably the convection oven will run a staged reflowprofile that will take the solder paste to the full reflowingtemperature. This operation may be carried out under an environment ofair or nitrogen.

After reflowing there will be solder flux residual left on the wafer.The flux residual is then removed using preferably an ultrasonicboard-cleaning machine. A preferred machine for removing the solder fluxresidual uses an appropriate solvent that is in a liquid sump at oneside of the machine and is held in vapour-phase at the other side of themachine. Preferably, the majority of the solder flux residual is removedin the liquid sump and the final clean is carried out in thevapour-phase. This process ensures that the wafers have very littlecontamination left thereon after cleaning. FIG. 17 illustrates a wafer53 having die therein prepared to include interconnects 19′,19″according to the present invention.

A paste according to the present invention is designed to substantiallyretain its shape as deposited after its binder has been reflown. Thus,for example, if the print aperture of the instrument for depositing thepaste forms a cube of a given height, then the interconnect formed afterreflowing the binder retains a form substantially similar to the shapeof the cube as deposited. It should be noted that there would inevitablybe some change in the shape after reflowing the binder. However, thechange in shape would not adversely affect the performance of theinterconnect.

After the power MOSFETs 40 in the wafer have interconnects 19′,19″formed on respective electrodes thereof, the wafer may be diced usingany available method of dicing, for example, sawing with standarddiamond impregnated blades, or laser sawing. The dicing results inindividual discrete power MOSFETs.

After power MOSFETs 40 have been singulated, each can be electricallyconnected to the interior surface of a respective can 48 by a conductiveadhesive, such as silver filled epoxy or solder, to form a package. Toperform this step each individual power MOSFET may be picked up by anautomatic pick and place machine and placed inside a respective can 48.The conductive adhesive, e.g. silver filled epoxy, may be depositedinside each can prior to placing a power MOSFET 40 therein. Afterplacing a MOSFET 40 inside a can 48 a curing step is carried out to curethe conductive epoxy.

It should be noted that the pick tips of a conventional pick and placemachine may have to be modified to clear interconnects 19′,19″. Apartfrom the modified pick-up tips, the pick and place step can be carriedout according to conventionally known techniques.

It should be noted that while silver filled epoxy is preferred othermaterials such as soft solders, or new conductive materials based oncarbon and graphite may be used without deviating from the presentinvention. In addition, electrically isolating die-attach materials suchas epoxies or polyimides may also be used in instances when electricalconnectivity is not desired. For example, when a power IC is disposedwithin a can by itself or with a power device, when a lateral power ICor a flip-chip power device is used, or when multiple devices aredisposed in a common can an insulating die-attach material may be usedto electrically insulate one or more of the devices from the can, whilestill taking advantage of its thermal properties.

As is known, a purpose of can 48 is to form the third connectionnecessary for the current through power MOSFET 40. This connection isgenerally required in this type of device to provide a good path forboth thermal and electrical conduction. Currently, the materialpreferred for can 48 is copper but other metals may also be considered.In addition to metals, metal matrix or composites as well as carbon andgraphite materials may be utilized to form this connection. The form andfunction of can 48 may also vary from application to application.

According to one aspect of the present invention, can 48 includes a goldlayer as its exterior finish. This is an improvement over some prior artpackages in which the can is finished with silver. It has been foundthat due to ionic migration silver on the can will promote dendriteformation between the can and the semiconductor device containedtherein, thereby shorting the two and rendering the package inoperative.Finishing can 48 with gold avoids such a problem. In a preferredembodiment, the gold finish may be 0.05-0.2 μm thick and it may beimmersion deposited on the can.

It should be noted that a package according to FIG. 12 is formed afterthe conductive epoxy is cured. However, to form a package according tothe variation shown by FIG. 13, the material for forming passivation 50is deposited over exposed portions of MOSFET 40 through single-needledispensing, multi-needle dispensing, or jetting technology, which is amore accurate and flexible approach. After depositing the passivationmaterial, a curing step is carried out to form passivation 50.

It should be noted that it is not necessary for passivation 50 toterminate at walls 49 of can 48. Rather, passivation 50 may be extendedover walls 48, especially when ink jet technology is employed to depositpassivation 50. The extension of passivation 50 over walls 49 of can 48will further increase the tracking distance.

Thus, to summarize, a process for manufacturing a package as shown inFIGS. 12 and 13 includes the following sequence of steps:

Passivate wafer with organopolysiloxane, or another suitablepassivation.

Print wafer with paste according to the present invention.

Reflow paste on wafer.

Clean flux residual.

Dice wafer.

Die bond to the interior of can.

Cure conductive adhesive to attach die.

Deposit passivation material (second variation) (edge of die, gapbetween the die and can, edge of can).

Cure passivation material (second variation).

Alternatively, the conductive adhesive for bonding the die to the canmay be a solder. If so, the process may include a cleaning step afterthe solder is reflown.

The following can be yet another alternative process for manufacturing apackage according to the present invention.

Passivate wafer with organopolysiloxane material, or any suitablepassivation.

Dice wafer.

Die bond to interior of can with conductive adhesive.

Cure die bond adhesive.

Deposit paste on die surface electrodes.

Reflow paste on electrodes.

Clean flux residual.

Deposit organopolysiloxane material (edge of die, gap between the dieand the can, and edge of can).

Cure passivation.

Alternatively, the conductive adhesive for bonding the die to the canmay be solder. In this case, however, no extra flux cleaning will berequired in that both the solder and the paste according to the presentinvention are reflown in the same step.

A package according to the variation shown by FIG. 13 is more ruggedthan the prior art package (see FIG. 15) due at least in part to arecessed die that is thickly coated with a passivation layer which ishighly resistant to both chemical and mechanical damage. Furthermore, arelatively thick interconnect formed from a paste according to thepresent invention also now serves to protect the contact areas of thedie, i.e. the gate electrode and the source electrode.

Also, the increased solder contact height and the combination ofmaterials used in the formation of an interconnect according to thepresent invention, and the secondary soldering process, result inimprovements in thermal cycling.

Furthermore, the process for manufacturing of a package according to thevariations shown in FIGS. 12 and 13 allows for the use of more diverseconstruction materials compared to the prior art technique, which meansit is now possible to easily produce a device using a can 48 as shownherein, and as existing in the prior art, which has no exposed silver.That is, passivation 50 can cover and thus seal the silver within thepackage. Furthermore, when solder is used as die attach material insteadof silver epoxy, the silver may be effectively removed.

Moreover, having thinner die and larger contact areas will enableimproved ON resistance and thermal performance over the prior art.

In addition, the thickness of the die does not have to match the depthof can 48. Thus, a die having a thickness that is different from thedepth of can 48 may be packaged within the same can as that used in theprior art when an interconnect according to the present invention isused to bring all die related terminations into the same plane.

Also, a package according to the variation shown in FIG. 13, gainsgreater distances between contacts and areas of different potential,which allows for higher voltage die compared to the prior art.

An additional advantageous result is that a greater area of the die cannow be utilized for connection in that the contacts, e.g. the gateelectrode and the source electrode, can be moved much closer to the edgeof the die than was previously possible in the prior art. As a resultlower ON resistance can be achieved, as a reduction in top metalspreading resistance will be realized. More importantly the boundary ondie size dictated as a result of current densities within the solderjoint will be favorably moved.

In an alternative embodiment, the formation of interconnects 19 can beapplied to electrode of a flip-chip type MOSFET 41, which includes adrain electrode 46, as well as, gate electrode 44 and source electrode42 on the same surface. An example of such a device is illustrated byFIG. 16. It should be noted that advantageously a flip-chip type powerMOSFET 41 may also be manufactured at wafer level, and then singulatedprior to packaging.

Referring now to FIGS. 18A-B, in a package according to the prior artthe connection between an electrode of a die and a conductive pad on acircuit is made through a solder mass 57 (FIG. 18A). Thus, the die mustbe roughly the depth of can 48 so that it may be coplanar withconnection surfaces 51. As a result, the thickness of the die is limitedby the depth of can 48. On the other hand, when an interconnect 19′,19″according to the present invention is used (FIG. 18B), the depth of can48 is no longer a limitation. Thus, thinner die may be used in a packageaccording to the present invention. Such a features makes it possible touse thin die such as IGBT die with cans 48 of the prior art depth. Also,it should be noted that when interconnects 19′,19″ are used there willbe a larger standoff between the die and the circuit board. For example,the standoff may be changed from 100 microns (solder mass 57 asconnector according to prior art) to 200 microns. The increase in thestandoff has been found to improve the fatigue resistance of the packagecompared to that of the prior art packages.

In yet another alternative embodiment, interconnects 19′,19″ can bereplaced with an interconnect formed from a solder alloy only whichextends through passivation 50, thus taking advantage of the beneficialproperties achieved by having passivation 50 as described herein. Thesolder alloy used may be tin-silver-copper alloy (e.g. 95.5% Sn, 3.8%Ag, 0.7% Cu (by weight)), tin-silver alloy (96% Sn, 4% Ag (by weight),or 90% Sn, 10% Ag (by weight)), or high lead solder alloy (95% Pb, 5% Sn(by weight)).

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

1. A semiconductor package comprising: a semiconductor device having afirst electrode on a first surface thereof, and a second electrode on asecond opposing surface thereof; a conductive can, said conductive canincluding an interior portion and at least one wall that surrounds saidinterior portion, said wall including an external connection surfaceadapted for external electrical connection; a conductive adhesivedisposed between said first electrode and said interior portion toelectrically and mechanically connect said interior portion to saidfirst electrode, whereby said semiconductor device is attached to saidinterior portion and spaced from said at least one wall; an electricallyconductive interconnect structure electrically and mechanicallyconnected to said second electrode; and a passivation layer formed oversaid second electrode, and disposed within a space between saidsemiconductor device and said at least one wall, wherein saidinterconnects extend through said passivation structure.
 2. Asemiconductor package according to claim 1, wherein said passivationstructure is comprised of a silicon based polymer.
 3. A semiconductorpackage according to claim 1, wherein said can is comprised of copper.4. A semiconductor package according to claim 1, wherein semiconductordevice is either a power MOSFET, a diode or an IGBT.
 5. A semiconductorpackage according to claim 1, wherein said conductive adhesive is eithersolder or conductive epoxy.
 6. A semiconductor package according toclaim 1, wherein said electrically conductive interconnect structure iscomprised of electrically conductive particles glued to one another by aconductive binder.
 7. A semiconductor package according to claim 6,wherein said binder is comprised of solder.
 8. A semiconductor packageaccording to claim 7, wherein said solder is comprised of tin-silversolder.
 9. A semiconductor package according to claim 8, wherein saidtin-silver solder is a composition substantially consisting of 95.5% Sn,3.8% Silver, and 0.7% Cu by weight.
 10. A semiconductor packageaccording to claim 7, wherein said solder is a composition substantiallyconsisting of 95% Sn and 5% Sb by weight.
 11. A semiconductor packageaccording to claim 7, wherein said solder is a high lead solder.
 12. Asemiconductor package according to claim 7, wherein said solder is atin-lead solder.
 13. A semiconductor package according to claim 6,wherein said electrically conductive particles are spherical.
 14. Asemiconductor package according to claim 6, wherein said electricallyconductive particles are cubical.
 15. A semiconductor package accordingto claim 6, wherein said electrically conductive particles areparallelepipeds.
 16. A semiconductor package according to claim 6,wherein said electrically conductive particles are comprised of copper.17. A semiconductor package according to claim 6, wherein saidelectrically conductive particles are plated with a nickel barrier. 18.A semiconductor package according to claim 6, wherein said electricallyconductive particles are passivated with tin.
 19. A semiconductorpackage according to claim 6, wherein said electrically conductiveparticles are passivated with silver.
 20. A semiconductor packageaccording to claim 6, wherein said electrically conductive particles arecomprised of nickel.
 21. A semiconductor package according to claim 6,wherein said electrically conductive particles are comprised of tinsilver.
 22. A semiconductor package according to claim 6, wherein saidelectrically conductive particles are comprised of tin-bismuth.
 23. Asemiconductor package according to claim 1, wherein said electricallyconductive binder comprises 50-85% of the total weight of saidinterconnect, and said electrically conductive particles comprise 5-40%of the total weight of said interconnect.
 24. A semiconductor packageaccording to claim 20, wherein said electrically conductive particlesare 15 μm-65 μm in size.
 25. A semiconductor package according to claim1, wherein said passivation extends over said at least one wall.
 26. Asemiconductor package comprising: a semiconductor device having a firstelectrode on a first surface thereof and a second electrode on a secondopposing surface thereof; a conductive can, said conductive canincluding an interior portion and at least one wall, said wall includingan external connection surface adapted for external electricalconnection; a conductive adhesive disposed between said first electrodeand said interior portion to electrically an mechanically connect saidinterior portion to said first electrode, whereby said semiconductordevice is attached to said interior portion and spaced from said atleast one wall; and an electrically conductive interconnect structureelectrically and mechanically connected to said second electrode;wherein said electrically conductive interconnect structure includes aplurality of conductive particles glued together by an electricallyconductive binder.
 27. A semiconductor package according to claim 26,wherein said electrically conductive binder comprises 50-85% of thetotal weight of said interconnect, and said electrically conductiveparticles comprise 5-40% of the total weight of said interconnect.